Hematology 107
51. Which clotting tests measure which portions of the coagulation cascade? Which med-
ications affect these tests?
PT (prothrombin time) measures the function of the extrinsic clotting pathway (prolonged by
warfarin), activated PTT (partial thromboplastin time) measures the function of the intrinsic clot-
ting pathway (prolonged by heparin), and BT (bleeding time) measures platelet function (pro-
longed by aspirin).
52. How do specific diseases affect clotting tests? What are the main differential points?
PLATELET RBC
DISEASE PT PTT BT COUNT COUNT OTHER
Von Willebrand's Normal High High Normal Normal Autosomal dominant
disease (look for family history)
Hemophilia A/B Normal High Normal Normal Normal X-linked recessive, A =
low factor 8, B = low
factor 9
DIG High High High Low Normal/ Appropriate history, low
low level of factor 8
Liver failure High High Normal Normal/ Normal/ Jaundice, normal factor 8
low low level; do not give vitamin
K (ineffective); use FFP
Heparin Normal High Normal Normal/ Normal Watch for thrombocyto-
low penia and thrombosis
Warfarin High Normal Normal Normal Normal Vitamin K antagonist
(factors 2, 7, 9, and 10)
IIP Normal Normal High Low Normal Watch for preceding URI
TIP Normal Normal High Low Low Hemolysis (smear), CNS
symptoms; treat with
plasmapheresis; do not
give platelets!
Scurvy Normal Normal Normal Normal Normal Fingernail and gum
hemorrhages, bone
hemorrhages; caused by
vitamin C deficiency
PT = prothrombin time, PTT = partial thromboplastin time, BT = bleeding time, RBC = red blood cell,
DIG = disseminated intravascular coagulation, ITP = idiopathic thrombocytopenic purpura, TTP =
thrombotic thrombocytopenic purpura, FFP = fresh frozen plasma, URI = upper respiratory infection,
CNS = central nervous system.
53. What are the common causes of thrombocytopenia? What kind of bleeding problems
are caused by low platelet counts?
Common causes of thrombocytopenia include purpura (idiopathic or thrombotic), hemolytic
uremic syndrome, disseminated intravascular coagulation, HIV, splenic sequestration, heparin
(treat by first stopping heparin), other medications (especially quinidine and sulfa drugs), autoim-
mune disease, and alcohol. Bleeding from thrombocytopenia is in the form of petechiae, nose
bleeds, and easy bruising.
54. What causes petechiae or "platelet-type" bleeding in the setting of normal platelets?
Vitamin C deficiency (scurvy) causes bleeding similar to that seen with low platelets (splin-
ter and gum hemorrhages, petechiae); perifollicular and subperiosteal hemorrhages are unique to
scurvy. Patients have a poor dietary history (the classic example is hot dogs and soda or tea and
toast), myalgias and arthralgias, and capillary fragility (bleeding is due to collagen problems in
the vessels). Treat with oral vitamin C.
Other causes include uremia (platelet dysfunction), inherited connective tissue disorders (Ehlers-
Danlos syndrome, Marian's syndrome), and chronic corticosteroid use (causes capillary fragility).
